Photographic paper



. AFehn, 1947.

MELT coAT/NG 0F BuTYR/c Ac/D ESTER OFCELLULOSE HAL/DE EMULS/ON BARYTA COAT/NG HOLLIS T. @ALLEY INI/ENTQR Patented Feb. ll, 1947 NITED STATES PATE PHTGRAPEHC PAPER Application March 30, 1945, Serial No. 585,5991/,

6 Claims.

My invention relates to the preparation of photographic paper in which the paper support is waterproof. This invention constitutes an improvement over the photographic paper described and claimed in my Patent No. 2,366,723. This application relates back to the application into which my patent matured as to any subject matter which is common to both applications.

in the preparation of photographic paper as described in my previous application, it was necessary in order to baryta coatV melt-coated paper to employ an organic solvent to soften the surface of the melt coating and thus cause adherence of the baryta coating thereto. My present invention constitutes an improvement thereover in that the use of an organic solvent or as a matter of fact any diluent is unnecessary in causing the adherence of the melt coating and the baryta coating.

One object of my invention is to provide a more simple and direct method of preparing photographic paper in which the paper support has been waterproofed than is possible in accordance with the invention described in my previous application. Other objects of my invention will appear herein.

Photographic papers in which the paper support is resistant to the effects of water or processing solutions satisfies a particular need in the photographic art. For instance, there are calls in the trade -lor pictures in nished form very shortly after the exposure of photographic lm, particularly found in what are commonly known c an 10e stores. Also, in military operations, it is often desirable that a dry, finished print be available for use very shortly after exposed film is brought to the processing station. In the case of ordinary photographic papers, it is primarily the paper support which retains the water from the washing baths, and, therefore, obtaining of the dry, nished prints primarily involves a Wait for the drying of the paper support. Therefore, photographic paper in which the paper support is waterproof lls a real need in certain branches of the photographic art. My invention has for an object the supplying of paper for use in the instances cited and any other instances in the the photographic art where quick delivery of a photographic print is desired.

Another advantage of using waterproofed paper for rapidly turned out prints is that the waterproofing of the paper especially by melt- 'coating with cellulose ester compositions prevents penetration of the paper by the sodium thiosulfate or hypo upon treatment of the CII 2 print for the necessary time in the fixing bath. By thus minimizing or eliminating the taking on of hypo by the paper, the stability of the silver image is improved and the necessity of a long washing after the fixing operation is eliminated.

I have found that a suitable waterproof photographic paper may be prepared without the necessity of usingv solvents to cause adherence of a bartya coating to a melt coating if the paper is first baryta coated, such as with a suspension of blanc iiXe or barium sulfate in a binder, usually gelatin or some other compatible material of high molecular weight, such as a far hydrolyzed cellulose ester or a synthetic resin. After the baryta coating has been dried, a melt coating of a low viscosity butyric acid ester of cellulose and a plasticizer is applied to both sides of the paper. In this way, adherence is obtained between the melt coating and the baryta coating. By then applying a silver halide emulsion layer over the melt coating on the baryta coated side of the paper, a product is obtained which is especially suitable for use in cases where quick prints are desired, this having been accomplished without the necessity of using any organic solvent in the preparation of the photographic paper.

The attached drawing illustrates a photographic paper in accordance with my invention. This photographic paper is prepared by ilrst coating aY paper, particularly a high alpha-cellulose paper with a baryta coating, such' as is commonly employed in the art. 'Ine baryta coating may be either a dispersion of blanc fixe in gelatin or it may be a dispersion of blanc xe in a cellulose ester or a synthetic resin, the latter two types of baryta coatings being described and claimed in Clark Patent No. 2,358,056 and Clark Patent No. 2,346,008, granted April 4, 1944, After the barytacoating has been applied to the paper in the customary manner, such as by flowing the baryta composition onto the paper and drying by passing through heated rooms (noncalendered) or over hot rollers (calendered), the paper is subjected to melt coating by depositing on both sides thereof a molten composition consisting of a low viscosity butyric acid ester of cellulose and a plasticizer, particularly a composition such as described in Salo and Vivian application Serial Nos. 512,051 and 512,052, led November 27, 1943, or a composition as described in my Patent No. 2,366,723.- The melt coating process may be carried out as'described in Malm and Salo ap- .plicatonrSerial No. 275,484, led May 24, 1939,

such as by depositing a thin layer of the melt onto the surface of the paper.

The low viscosity butyric acid esters of cellulose which are employed in the melt coating operation in preparing photographic paper in accordance with my invention are those which have a melting point of less than 200 C., a char point of at least 260 C. and preferably at least 300 C. (indicating good stability), a fundamental cuprammonium viscosity of not more than l centipoises and an acetone viscosity within the range of to 100 centipoises, this viscosity being that of a solution of one part of ester in solution in 9 parts of acetone at 25 C. The cellulose ester should have a butyryl content of at least 42% and should be hydrolyzed little, if any. EX- amples of some cellulose esters having the properties stated above and suitable for melt coatings in the preparation of photographic paper in accordance with my invention are:

1. Cellulose acetate butyrate, butyryl content 47 .7 acetyl content 6.5%, acetone viscosity 24.9 centipoises.

2. Cellulose acetate butyrate, butyryl content 49.4%, acetyl content 5.6%, acetone viscosity 20 centipoises.

3. Cellulose acetate butyrate, butyryl content 48%, acetyl content 6.2%, acetone viscosity of 15 centipoises.

4. Cellulose acetate butyrate, butyryl content 52%, acetyl content 1.5%, acetone Viscosity 22 centipoises.

5. Cellulose butyrate, butyryl content 55%, i

y acetone viscosity 16 centipoises.

It is desirable that the plasticizer in the composition be -100% (based on the cellulose ester) the proportion of plasticizer employed being governed by the conditions of operation and the hardness desired in the melt coating. Further details as to the preferred melt coating process and compositions may be determined by reference to Salo and Vivian applications Serial Nos. 512,051 and 512,052.

After the melt coating has been applied, thereby waterprooing the paper, a photographic silver halide emulsion may then be applied which may be'either a gelatin emulsion or an emulsion in which a cellulose ester is employed as the carrier for the silver halide as described in Salo Patent No 2,110,491', granted March 8, 1938. It is preferred with some types of photographic emulsions that intermediate or subbing layers be employed to promote the adherence of the emulsion to themelt coating. One type of subbing which has been found to be useful in this connection is formed by rst applying a Very thinY layer of a cellulose nitrate of quite low viscosity to the melt coating followed by a very thin layer of gelatin applied thereto. The technique of subbing in this manner is described in U. S. Patent No. 2,014,547 of Babcock granted September 17, 1935. The disclosure of that patent may be referred to as a guide for this type of subbing operation. If desired, instead of using two layers, the nitrate and gelatin may be'mixed and applied as one layer. Instead of a nitrate layer one may employa layer of a mixed oellulose ester, such as hydrolyzed cellulose acetate propicnate. lis a matter of fact, any of the usual types of subbing layers which have been described in the prior art and which are compatible with the photographic emulsion layer to be employed and the melt coating surface, may

, referred to.

Vvlose butyrate of low plasticizer content.

4 be used if a subbing layer should be thought to be necessary.

In some cases photographic paper is dried quickly by subjecting to elevated temperatures. It is desirable in making paper of this type to apply a thin coating of a cellulose ester or synthetic resin to the paper from its solution in a solvent on the side opposite the baryta coating. Materials useful for this purpose are cellulose nitrate or hydrolyzed cellulose esters such as cellulose acetate, cellulose propionate or cellu- It is generally satisfactory to coat the backing layer fromY a solution of concentration of 1-5% of cellulose ester, the criterion as to the solvent used being that it is a solvent for the cellulose ester employed but not of the melt coating. Thus the sticking point may be raised from about 200 F. to 2SC-300 F.

The following examples illustrate my invention:

Example I Paper made from high alpha-cellulose wood pulp was coated on one side with a suspension of baryta (barium sulfate) in an aqueous gelatin solution and the coating was dried by passing the paper through a heated chamber. The sheet was then passed through a melt coating machine by which a coating of a cellulose ester melt composition containing 75% of cellulose acetate butyrate, 12.5% of dibutyl sebacate and 12.5% of diamyl phthalate was applied to the sheet on both sides.

The cellulose acetate butyrate used was a cellulose ester analyzing 38% butyryl and 12-14% acetyl and a viscosity of about 4 cps. measured at 25 C. in 10% acetone solution.

The coating Was accomplished by passing the paper between two heated rolls to which molten cellulose ester composition Was supplied which composition collected at the nip between the two rolls. The Weight of the coating is regulated by adjustment of the clearance between the rolls,

, by the temperature and viscosity of the composition and the speed of the machine.

The paper was melt-coated with the cellulose ester composition at the rate of 10 lbs. per 1000 sq. ft. of paper. It was then coated on the baryta side with a cellulose nitrate subbing layer and thereover a gelatin subbing layer in the manner described in the Babcock patent A gelatine silver halide emulsion was applied over the gelatin subbing layer and the product was complete. Adherence of the emulsion layer to the base was good under both wet and dry conditions. The paper was sufficiently waterproof to allow rapid processing and Washing.

Example II Paper made from high alpha cellulose wood -pulp was coated on one side with a'suspension of acetate was coated on the paper from organic solvent solution. A gelatin silver halide emulsion was applied over the gelatin subbing layer and a water resistantphotographic paper was obtained.

What I claim is:

1. A photographic paper which comprises a paper which has been baryta `coated on one side, then waterproofed by applying to both sides a melt coating of a low melting composition essentially consisting of a low viscosity .butyric acidV ester of cellulose and a plasticizer and to which a silver halide photographic emulsion has been applied over the melt coating on the baryta coated side of the paper.

2. A photographic paper which comprises a paper which has been baryta coated on one side, then waterproofed by applying to both sides a melt coating of a low melting composition essentially consisting of a low viscosity cellulose acetate butyrate and a plasticizer and to which a silver halide photographic emulsion has been applied over the melt coating on the baryta coated side of the paper.

3. A photographic paper which comprises a paper which has been baryta ycoated on one side, then waterproofed by applying to both sides a melt coating of a loW melting composition essentially consisting of cellulose acetate butyrate having a butyryl content of 47% and an acetyl content of 5%, the cellulose acetate butyrate making up '70% of the composition the remainder of which consists of 14% of dibutyl sebacate and 16% of butyl stearate, said photographic paper containing a silver halide photographic emulsion layer thereon applied over the melf, coating on the baryta coated side of the paper.

4. A method of preparing a photographic paper which `comprises applying a baryta coating to paper, then melt coating the paper on both sides with a low melting composition essentially consisting of a low viscosity butyric acid ester of cellulose and a plasticizer followed by applying a silver halide photographic emulsion over the melt coating on the baryta coated side of the paper.

5. A method of preparing a photographic paper which comprises applying a baryta coating to paper, then melt coating the paper on both sides with a low-melting composition, essentially consisting of loW viscosity cellulose acetate `butyrate and a plasticizer, followed by applying a silver halide photographic emulsion over the melt coating on the baryta coated side of the paper.

6. A method of preparing a photographic paper which comprises applying a baryta coating -to paper, tl'en melt coating the paper on both sides with a low-melting composition, essentially consisting of cellulose acetate butyrate and plasticizer, the cellulose acetate butyrate having a butyryl content of 47% and an acetyl content of 5%, the cellulose acetate butyrate making up 70% -of the composition and the plasticizer constituting the remainder, which plasticizer .consists of a mixture of dibutyl sebacate and butyl stearate, and then applying a silver halide photographic emulsion over the melt coating on the baryta coated side of the paper.

HOLLIS T. GALLEY. 

